Aerial Bait Drops to Reduce Invasive Brown Treesnakes

The brown treesnake (BTS) is an invasive species accidentally introduced to Guam in the late 1940s. With no native predators, the snake's population in Guam has grown to an estimated 1 to 2 million. The BTS is responsible for the extinction of most native bird, bat, and lizard species on the island. The BTS has also caused extensive economic damage to the island's economy and electrical grid. The unintentional movement of BTS as a result of shipping or travel represents a very real danger to all islands in the western Pacific basin and sections of the U.S. mainland. The economic costs of potential BTS colonization to the Hawaiian Islands alone are estimated to be as high as $2 billion annually--in addition to the severe ecological damage the snake would cause to native birds and other wildlife.

Since the late 1980s, the USDA Wildlife Services program and its research arm the National Wildlife Research Center (NWRC) have been actively involved in collaborative efforts to reduce the number of BTS on Guam and prevent the snake's spread. These have included a range of snake-trapping activities, the use of snake-detector dogs to search all outgoing cargo, research activities to develop new control methods and techniques, and an extensive public awareness program on Guam and other islands. It is a result of these successful Federal, State, and local cooperative efforts that no live BTS have been detected at Hawaiian ports-of-entry in almost 20 years, and more than 150,000 BTS have been removed from the transportation system in Guam.

In 2013 and 2014, NWRC researchers will be collaborating with the Department of Defense, the Department of the Interior, and the Guam Department of Agriculture to demonstrate and evaluate the use of aerial broadcast baits to reduce BTS numbers in remote and rugged areas of Guam. The goal of project is to significantly reduce the BTS population at targeted sites on military installations. The effects of the project will be documented and used to inform future efforts to control or eradicate the BTS population island-wide.

The new technique uses dead mice to deliver an 80-milligram acetaminophen tablet (an infant’s dose) placed inside each mouse carcass. The dead mice are fitted to a biodegradable streamer-like device designed to snag onto branches in the dense tree canopy where the snakes feed. Studies have shown that BTS scavenge and will readily eat dead mice. This demonstration project, which involves extensive monitoring of snake populations before and after bait drops, costs $1.3 million. Preliminary studies using the same technique have resulted in an 85 percent reduction of snake activity in treated areas. For more information on USDA's efforts to manage the invasive brown treesnake on Guam, please visit the following links: